Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753248Ab0HZRnB (ORCPT ); Thu, 26 Aug 2010 13:43:01 -0400 Received: from gir.skynet.ie ([193.1.99.77]:47277 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751985Ab0HZRm7 (ORCPT ); Thu, 26 Aug 2010 13:42:59 -0400 Date: Thu, 26 Aug 2010 18:42:45 +0100 From: Mel Gorman To: Minchan Kim Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Christian Ehrhardt , Johannes Weiner , Wu Fengguang , Jan Kara , linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] writeback: Do not congestion sleep when there are no congested BDIs Message-ID: <20100826174245.GJ20944@csn.ul.ie> References: <1282835656-5638-1-git-send-email-mel@csn.ul.ie> <1282835656-5638-4-git-send-email-mel@csn.ul.ie> <20100826173843.GD6873@barrios-desktop> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100826173843.GD6873@barrios-desktop> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3166 Lines: 78 On Fri, Aug 27, 2010 at 02:38:43AM +0900, Minchan Kim wrote: > On Thu, Aug 26, 2010 at 04:14:16PM +0100, Mel Gorman wrote: > > If congestion_wait() is called with no BDIs congested, the caller will > > sleep for the full timeout and this is an unnecessary sleep. This patch > > checks if there are BDIs congested. If so, it goes to sleep as normal. > > If not, it calls cond_resched() to ensure the caller is not hogging the > > CPU longer than its quota but otherwise will not sleep. > > > > This is aimed at reducing some of the major desktop stalls reported during > > IO. For example, while kswapd is operating, it calls congestion_wait() > > but it could just have been reclaiming clean page cache pages with no > > congestion. Without this patch, it would sleep for a full timeout but after > > this patch, it'll just call schedule() if it has been on the CPU too long. > > Similar logic applies to direct reclaimers that are not making enough > > progress. > > > > Signed-off-by: Mel Gorman > > --- > > mm/backing-dev.c | 20 ++++++++++++++------ > > 1 files changed, 14 insertions(+), 6 deletions(-) > > > > diff --git a/mm/backing-dev.c b/mm/backing-dev.c > > index a49167f..6abe860 100644 > > --- a/mm/backing-dev.c > > +++ b/mm/backing-dev.c > > Function's decripton should be changed since we don't wait next write any more. > My bad. I need to check that "next write" thing. It doesn't appear to be happening but maybe that side of things just broke somewhere in the distant past. I lack context of how this is meant to work so maybe someone will educate me. > > @@ -767,13 +767,21 @@ long congestion_wait(int sync, long timeout) > > DEFINE_WAIT(wait); > > wait_queue_head_t *wqh = &congestion_wqh[sync]; > > > > - /* Check if this call to congestion_wait was necessary */ > > - if (atomic_read(&nr_bdi_congested[sync]) == 0) > > + /* > > + * If there is no congestion, there is no point sleeping on the queue. > > + * This call was unecessary but in case we are spinning due to a bad > > + * caller, at least call cond_reched() and sleep if our CPU quota > > + * has expired > > + */ > > + if (atomic_read(&nr_bdi_congested[sync]) == 0) { > > unnecessary = true; > > - > > - prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE); > > - ret = io_schedule_timeout(timeout); > > - finish_wait(wqh, &wait); > > + cond_resched(); > > + ret = 0; > > "ret = timeout" is more proper as considering io_schedule_timeout's return value. > Good point, will fix. > > + } else { > > + prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE); > > + ret = io_schedule_timeout(timeout); > > + finish_wait(wqh, &wait); > > + } > > > > trace_writeback_congest_waited(jiffies_to_usecs(jiffies - start), > > unnecessary); -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/